Cyclopolymerization of 1,5-hexadiene was first reported by Marvel and Stille, and further investigated by Makowski. See Marvel, C.S. et al. "Intermolecular-Intramolecular Polymerization of .alpha.-Olefins by Metal Alkyl Coordination Catalysts", J. Am. Chem. Soc., 1958, 80, 1970 and Makowski, H.S. et al., "1,5-Hexadiene Polymers, I., Structure and Properties of Poly 1-5 Hexadiene", J. Polymer Sci., Part A, 1964, 2, 1549. Both studies utilized heterogeneous Ziegler-Natta catalysts which promote a special type of addition polymerization referred to as coordination polymerization. Marvel and Makowski both reported low activities and incomplete cyclization of the diolefin. More recently, Cheng reported that cyclo-polymerization of 1,5-hexadiene using a catalyst system of diethylaluminum chloride and titanium trichloride. .sup.13 C-NMR analysis of the resulting polymer indicated complete cyclization and an approximate 1:1 ratio of tran- and cis-fused cyclopentane rings in the polymer. Cheng et al., ".sup.13 C-NMR Characterization of Poly(1,5-hexadiene)", J. Appl. Polym. Sci., 1988, 35, 825.
One of the special features of Ziegler-Natta catalysts is the stereochemistry associated with polymerization. Radical- and cationic-chain polymerization of monosubstituted olefins lead to products having random stereochemical configuration, referred to as atactic polymers. Regular stereoisomers are possible, and some Ziegler-Natta catalysts promote formation of stereoregular polymers. Isotactic polymers of .alpha.-olefins are those having the same stereochemistry at each asymmetric carbon and syndiotactic polymers are those where the configuration alternates regularly down the chain. For instance, Ziegler-Natta catalysts have produced isotactic, syndiotactic and atactic polypropylenes.
Bis(cyclopentadienyl) bis(phenyl) titanium/methylalumoxane was reported as the first homogeneous catalyst system to influence and control the stereochemistry of propylene polymerization. Ewen, J.A., "Mechanisms of Stereochemical Control in Propylene Polymerizations with Soluble Group 4B Metallocene/Methylalumoxane Catalysts", J. Am. Chem. Soc., 1984, 106, 6355. More recently, it was reported that homogeneous zirconium catalysts produced isotactic polypropylene and polybutene. Kaminsky, W., et al., "Polymerization of Propene and Butene with a Chiral Zirconocene and Methylalumoxane as Cocatalyst", Angew. Chem. Int. Ed. Engl., 1985, 24, 507.